The research has five technical and five theoretical goals. The technical goals are (a) a thorough study of the diagnostic efficiency an item response characteristics of all diagnostic criteria in the six recent diagnostic systems (DSM-III, DSM-III-R, DSM-IV, ICD-9, ICD-10, ASAM); (b) studies of the concurrent validity of DSM-IV and ICD-10 with independent illness validators; (c) studies of the predictive validity of the DSM-IV and ICD-10 algorithms by both summary severity score and critical items, with multiple indices of 6- and 12-month outcomes; (d) studies in severity scaling by the major systems (DSM and ICD). including item difficulty, inter-item consistency and distributional analysis of summary algorithm scores; and (e) development of experimental, minimal, and drug-customized diagnostic algorithms through the use of criterion weighting schemes based on prior research. Theoretical goals include (a) research on the construct validity of the DSM-IV and ICD-10 approaches to drug dependence, and more importantly the construct validity of the Alcohol Dependence Syndrome on which they are based through two pathways - factor-analytic research, and the longitudinal, illness-staging method; (b) research on the construct validity of the drug abuse category through the same methods; (c) research on developmental pathways into drug and alcohol dependence through the examination of prodromal course and illness onset; (d) the study of individual differences variables such as age, gender, period cohort, and special population effects, in the diagnostic data; and (e) an integrated approach to describing stable subsample differences by subtyping and comorbidity studies.